Portable electronic devices, such as those configured to be handheld or otherwise associated with a user, are employed in a wide variety of applications and environments. The ubiquity of devices such as mobile phones, smart phones, and other similar devices indicates the popularity and desire for these types of devices. Increasingly, such devices are equipped with one or more sensors or other systems for determining the position or motion of the portable device, including inertial navigation techniques based upon the integration of specific forces and angular rates as measured by inertial sensors (e.g. accelerometers, gyroscopes).
Often, such portable devices may be associated with a platform that transports the device, as in the example of a mobile/smart phone being carried by a person. Although the portable device generally may be transported in the direction of movement of the platform, its orientation is typically not constrained, resulting in a misalignment of a heading between the device heading and the platform heading. The heading misalignment is the difference between the frame aligned with the portable device and the frame aligned with the platform. As in the example of a mobile phone, it may be held in the user's hand and employed in a variety of orientations relative to the user.
Alignment of the inertial sensors within the platform (e.g., alignment of the portable electronic device containing the inertial sensors with the platform's forward, transversal and vertical axes) is typically required for traditional inertial navigation systems. Where the inertial sensors are not properly aligned, the positions and attitude calculated using measurements from the inertial sensors will not be representative of the state of the platform. As such, in order to achieve high accuracy navigation solutions, inertial sensors must be tethered within the platform. As presented above, portable electronic devices, however, are able to move relative to a user, whether constrained or unconstrained within the platform, and careful mounting or tethering of the device to the platform is not an option. Accordingly, knowledge of misalignment is a key factor in enabling an accurate navigation solution.